The invention relates to a steering gear according to the preamble of claim 1 and to a steering system equipped therewith. The invention in particular relates to a steering gear which is designed as a helical gear mechanism or a worm gear mechanism for an electric power steering system.
A steering gear of the type in question in the form of a helical gear mechanism for use in an electric power steering system is known from DE 101 61 715 A1. FIG. 1 shows the known helical gear mechanism 1, which is designed as a worm gear mechanism comprising a housing 2, in which a worm 3 and a worm gear 4 are disposed, wherein the worm 3 is connected by means of a coupling 8 to the drive shaft 9 of an electric drive motor 10, the shaft being mounted in a bearing 11. In this known design, the worm shaft is mounted in a shaft bearing 5, which comprises a ball bearing 6 in the form of a four-point bearing and is designed as a swiveling bearing, whereby the interlocking play between the worm 3 and the worm gear 4 can be kept constant during the entire service life of the gear mechanism. For this purpose, a preload force acts radially on the worm 3 and the worm is permanently pressed against the toothing of the worm gear 4 or helical gear. This is done by means of a preload device, which comprises a preload spring 13 and a pressure device 12 so as to cause engagement between the worm 3 and the worm gear 4 without play, and compensate for the operating forces that occur. The pressure device 12 can, for example, be provided with a hydraulic device 14 and a pressure piece 15 actuated thereby, the pressure piece directly acting on the bearing 16 or the worm 3. This allows for the wear which occurs over the service life to be automatically compensated for, whereby the tooth flank play is not increased to the extent possible and vibration noise is prevented. However, it has been shown such a known design may also create noise at the shaft bearing 5, wherein the noise can be eliminated here only conditionally through the use of an expensive specialty bearing.
DE 602 10 154 T2 describes a steering system comprising a worm gear mechanism. The design described there likewise comprises a fixed bearing, which is configured as a pivot bearing. The floating bearing likewise comprises a pressure piece. As a result, a customary steering gear comprising a helical pinion or worm is described here as well.
At the drive-side end, these customary steering gears comprising helical pinions (worm) thus comprise a shaft bearing configuration designed as a fixed bearing, in which a first rolling bearing (ball bearing) is provided. At the free end of the helical pinion (worm), a bearing device, which is designed as a floating bearing and comprises a second rolling bearing, is provided. This is intended to prevent, or at least drastically reduce, the development of noise, as efficiently as possible, both on the fixed bearing side and on the floating bearing side.
In addition, shaft bearing configurations comprising rolling bearings or ball bearings are known, in which the outer ring of the ball bearing is received in a sliding bearing, or in which the inner ring of the ball bearing is received in what is known as silent bushings, whereby the shaft is likewise pivotably mounted. However, these solutions are complex to implement and have relatively large play, which in turn results in the development of noise, notably during load changes (changes in steering). Moreover, these shaft bearing configurations are susceptible to temperature fluctuations and the service life thereof is not long.
The published patent application FR 2 891 036 describes a steering system comprising a recirculating ball steering gear, in which the shaft bearing configuration (see FIGS. 3-6 there) is improved by means of a mounting produced from one material, whereby two annular sections (24 and 25) are formed, which are connected to each other solely via narrow lands (26), wherein the inner annular section receives the rolling bearing for the shaft bearing configuration and the outer annular section is installed in the housing. Because of the narrow lands, the inner section can be easily pivoted relative to the outer section (see FIG. 6), whereby certain elasticity is attained in the shaft bearing configuration of a recirculating ball gear. A connection to helical gear mechanisms is not established there.
However, the focus in modern steering systems comprising helical gear mechanisms must be increasingly directed to improved noise reduction and effective mechanical action (interlocking).